1. Field of the Invention
The present invention relates to a display board by which a voluntary colored picture is formed on a substrate. Such a display board is used as a dial board or the like of a tachometer on a speedometer of a vehicle, for example.
2. Description of the Prior Art
Letters, figures or the like on a dial board of a meter are conventionally formed on a resin substrate by printing, especially by screen printing. The screen printing enables the printing of a thick paint film to provide a deep picture.
However, the above screen printing uses liquid ink diluted by solvent and therefore cause problems of contamination of the working environment, and fire due to the evaporation of the solvent within the ink, requiring a time for removing ink from a printing plate clogged therewith and controlling the viscosity of ink. This also requires special skill in controlling these operations, or the like.
Accordingly, recently, a photopolymerization ink containing no solvent and setting in a short time has been proposed. This photopolymerization ink takes advantage of the photosetting property of the photopolymerization resin. It has low viscosity and high fluidity before light irradiation and therefore does not require any solvent.
However, this photopolymerization ink requires the addition of reactant type diluent (for a monomer of low molecular weight) in order to adjust the viscosity thereof so as to be properly suited to the screen printing. This diluent functions similarly to the solvent, so that the unreacted substance gradually evaporates from the paint film. Moreover, the photopolymerization ink is of a low molecular weight as a whole and therefore has problems of large scale shrinkage due to setting, shortage of adhesion, lack of flexibility, or the like. In addition, the production cost is expensive so that photopolymerization ink is insufficient for practical use.
Moreover, multicolor printing has been desired in order to improve the appearance of the dial board, and the visibility thereof. In order to satisfy the above desire, the conventional screen printing uses printing plates and inks of the same number as the number of colors. This results in a troublesome producing processes and as increased production cost.
Meanwhile, offset printing has been mainly adopted as the multicolor printing in the printing trade. However, in applying this offset printing to a display board, this offset printing has also problems that ink is liquid, the color density of each printing plate is insufficient, or the like.